The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders.
The spine includes seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region. While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow shaft containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae.
The spinal disks act as shock absorbers, cushioning the spine, and preventing individual bones from contacting each other. Disks also help to hold the vertebrae together. The weight of the upper body is transferred through the spine to the hips and the legs. The spine is held upright through the work of the back muscles, which are attached to the vertebrae. While the normal spine has no side-to-side curve, it does have a series of front-to-back curves, giving it a gentle “S” shape. If the proper shaping and/or curvature are not present due to scoliosis, neuromuscular disease, cerebral palsy, or other disorder, it may be necessary to straighten or adjust the spine into a proper curvature.
Generally the correct curvature is obtained by manipulating the vertebrae into their proper position and securing that position with a rigid system of screws, rods, intervertebral spaces, and/or plates. The various components of the system may be surgically inserted through open or minimally invasive surgeries. The components may also be inserted through various approaches to the spine including anterior, lateral, and posterior approaches and others in between.
Spinal fixation systems may be used in surgery to align, adjust, and/or fix portions of the spinal column, i.e., vertebrae, in a desired spatial relationship relative to each other. Many spinal fixation systems employ a spinal rod for supporting the spine and for properly positioning components of the spine for various treatment purposes. Vertebral anchors, comprising pins, bolts, screws, and hooks, engage the vertebrae and connect the supporting rod to different vertebrae. The size, length, and shape of the cylindrical rod depend on the size, number, and position of the vertebrae to be held in a desired spatial relationship relative to each other by the apparatus.
During spinal surgery, a surgeon first exposes the spine posterior and attaches the vertebral anchors to selected vertebrae of the spine. The surgeon then inserts a properly shaped spinal rod into rod-receiving portions of the vertebral anchors to connect the selected vertebrae, thereby fixing the relative positions of the vertebrae. Generally, a controlled mechanical force is required to bring together the spinal rod and a spinal implant, such as the vertebral anchors, in a convenient manner. After insertion, a surgeon must insert a locking mechanism, such as a set screw, into the vertebral anchor to lock the spinal rod to the implant after the force for inserting the rod is removed.
Patients suffering from orthopedic injuries, deformities, or degenerative diseases often require surgery to stabilize an internal structure, promote healing, and/or relieve pain. In the spinal field, surgeries to correct spinal abnormalities often involve positioning one or more elongate stabilization elements such as rods, plates or other types of elongate members along a portion of the spinal column, and anchoring each of the elongate stabilization elements to two or more vertebrae via screws, hooks or other types of bone anchors. Prior to anchoring the elongate stabilization element to the spinal column, the surgeon may need to measure the distance between the bone anchors or between two reference locations along the spinal column in order to determine the appropriate length of the elongate stabilization element. In some instances, the bone anchors may be arranged at varying angular orientations, thereby presenting difficulties in accurately measuring the distance between the bone anchors to provide a properly sized elongate stabilization element having a length sufficient for coupling to the bone anchors.
Certain spinal conditions, including a fracture of a vertebra and a herniated disc, indicate treatment by spinal immobilization. Several systems of spinal joint immobilization are known, including surgical fusion and the attachment of pins and bone plates to the affected vertebrae. Known systems include screws having proximal heads and threaded shafts that may be inserted into at least two spaced-apart vertebras. Each screw includes a receiver attached over the head such that a stabilization rod can interconnect two or more receivers to immobilize the vertebras spanned by the screws.
Spinal immobilization systems typically require the threaded securement of some form of bone anchor and the like or bone screw-assembly into two or more vertebrae, which entails the drawing of the rod to the anchors/screw-assemblies, or drawing the anchors/screw-assemblies to the rod. Spinal screw-assemblies are used to secure a stabilization rod and comprise various components including a pedicle screw and a body member. The design of the spinal screw-assemblies allows for variable angular movement of the body member with respect to the pedicle screw with a threaded shaft portion of the screw extending through an opening in an end of the body member. However, in these systems, in order to tighten the spinal screw-assembly at a specific angle, a rod and a set screw must first be inserted, the components are tightened, and then the rod and set screw are removed.
The present invention helps to expedite the time of surgery by allowing a medical professional to provisionally tighten the spinal screw-assembly at a specific angle prior to placing a rod or set screw into the body member.